The vaporizing unit of the present invention is similar in some structural respects to the vaporizing unit described in Copending Application Ser. No. 5,146 which was filed Jan. 20, 1987 in the name of the present inventor.
The prior art vaporizers, for the most part, use steam to vaporize a medication or other substance, so that the medication may be raised to a constant vaporizing temperature, the boiling point of water and held at that temperature only while water is available to be boiled in the reservoir of the vaporizer. However, this means that the medicinal effects, for example, of the vaporized substance are diluted by the steam. The presence of steam may have disadvantages or advantages to achieving the desired medicinal effects. The vaporizer of the present invention, like the vaporizer of the Copending Application, provides a dry vaporizing action by which the medication, or other substance to be vaporized, is vaporized directly at the most appropriate vaporizing temperature for a period of time that is only dependent on the electrical supply, and operates in an undiluted manner.
The vaporizing unit of the invention, in one of its embodiments, like the unit described in the Copending Application, uses paraffin wax, or the like, to transmit the heat from the heating elements to a compressed paper fiber pad impregnated with the substance to be vaporized so that a predetermined temperature may be established for the pad which remains constant over prolonged periods of time.
When the substance to be vaporized from the pad is a liquid, such as a medication, insecticide or perfume, it is absorbed into the pad, which is usually a compressed paper fiber pad. Examples of such commercially available pads for pesticide applications include "Pif-Paf" marketed by The Wellcome Foundation Ltd., Berkhamsted, Hertfordshire, England; "Revenge" marketed by Aeroxon Products, Inc., New Rochelle, N.Y., U.S.A.; and "Vape Mat F" marketed by Fumakilla Ltd., Tokyo, Japan.
These pads are usually manufactured from a large sheet of compressed paper fiber with a final thickness of about 1/8th of an inch. Prior to compression the paper fiber pulp may have a thickness of as much as 3/8ths of an inch. The force involved in the compression tends to align the long dimension of the paper fibers at right angles to the applied force, that is to say along the length of the pad with the small cross section of the fibers towards the edges of the pad. These large pads are then cut to the required dimensions for use in the appropriate vaporizer and are impregnated with the liquids to be vaporized and other components of the product formulation.
Vaporizers of the type disclosed in the Copending Application Ser. No. 005,146 apply heat to only one of the large faces of the pad. Such vaporizers are currently the only ones in commercial use.
Experimentation with that type of vaporizer showed that as one of the faces of the pad was heated, liquids impregnated in the pad tended to move to the edges of the pad rather than to the exposed face which was not heated. The impregnated liquid was found to move along the long axis of the compressed fibers by capillary action which was initiated by thermal diffusion. Only small amounts of impregnated liquid were found to move to the unheated face of the pad since the alignment of the fibers prevented capillary action and therefore movement was solely by thermal diffusion. This resulted in an inactive "dead space" in the pad under the unheated face and impregnated liquid trapped in this area did not contribute significantly to vaporization. The practical result of these findings was that the unheated face of the pad was significantly colder than the heated face and that vaporization of the impregnated liquid occurred mainly at the edges of the pad, with very little release of vapor from the unheated face.
The vaporizing unit of this invention greatly increases the vaporizing efficiency of the pad by heating it from both faces. Such a vaporizer has the distinct advantage over the vaporizer of the Copending Application in that when operating at a given temperature more heat energy is introduced into the pad, and the pad does not have a "cold" face. Heating both faces of the pad increases the rate of thermal diffusion of the impregnated liquid within the pad and its movement to the edges of the pad by capillary action. Therefore more impregnated liquid is available at the edge of the pad for release and vaporization.
Vaporizing units of the type disclosed in this invention have several other advantages over those currently available that only heat one face of the pad. They have a more even vapor release pattern, with the initial release of the active components occurring more rapidly and continuing for longer periods at a more steady level. This occurs because more of the active component can move to the edges of the pad when it is heated from both sides as there is no impregnated liquid trapped in an inactive "dead space" in the pad under an unheated face.
The double sided vaporizing unit of the invention is safer to use than the unit of the Copending Application since it can operate at a lower temperature, providing that the temperature is above vaporization temperature of the active component to be released from the pad, since it applies more heat energy more evenly to the pad. Operating the vaporizing unit at a lower temperature also has the advantage of reducing any thermal degradation of the impregnated liquids that could reduce their activity and increase any toxicity caused by the products of such degradation.